VVVF frequency conversion, vector control frequency conversion, and direct torque control frequency conversion are all one of the AC-DC-AC frequency conversion. One of the disadvantages is that the input power factor is low, the harmonic current is large, the DC circuit requires a large energy storage capacitor, and the regenerative energy cannot be reflected back to the grid, that is, it cannot carry out four-quadrant operation. For this reason, matrix alternating frequency-alternating frequency came into being. Because the matrix AC-AC frequency conversion eliminates the central DC link, the large and expensive electrolytic capacitors are eliminated. It can achieve a power factor of L, an input current of sinusoidal and four-quadrant operation, and a large power density of the system. Although this skill is not mature now, it still attracts many scholars to study it in depth. Its essence is not to indirectly manipulate the current and flux, but to directly use the torque as the quantity to be manipulated. Here's how:
1. Control the stator flux to introduce the stator flux observer to realize the speed sensor-free mode;
2. Automatic identification (ID) relies on the first-class motor mathematical model to automatically identify motor parameters;
3. Calculate the practical value corresponding to the stator impedance, mutual inductance, magnetic full element, inertia, etc., and calculate the practical torque, stator flux, and rotor speed for real-time control;
4. Realize Band-Band control, and PWM signal is generated by Band-Band control of magnetic flux and torque, and control the inverter switching status.
Matrix alternating frequency conversion has fast torque response (<2ms), high speed accuracy (±2%, no PG reaction), and high torque accuracy (<+3%). At the same time, it also has high starting torque and high torque accuracy, especially at low speed (including 0 speed), it can output 150%-200% torque.
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